Interpretive Summary: “Candidatus Liberibacter solanacearum” is a putative bacterial pathogen of potato zebra-chip disease threatening the potato industry in the United States and other countries. Currently, the bacterium cannot be cultured in artificial media. Little is known about the bacterial biology. In this study, “Ca. L. solanacearum” was enriched in tomato plants and examined under scanning electron microscope. Rod, spherical, and variable shapes of cells were found. This is the first description of the multiple shapes of the bacterium. The new information expands current knowledge about this bacterium and will facilitate future research efforts.

Technical Abstract:
“Candidatus Liberibacter solanacearum” is an alpha-proteobacterium associated with potato zebra-chip disease. The bacterium is currently non-cultureable. Very little is known about the bacterial morphology, an important characteristic of a complete bacterial description. In this study, “Ca. L. solanacearum” was examined by scanning electron microscopy in tomato phloem tissues where the bacterial cells were enriched. Bacillus, coccus, and pleomorphic bacterial cells were observed in phloem cells of infected tomato petioles. A preliminary analysis suggested that the different morphological types might reflect various life stages of “Ca. L. solanacearum”. The new information increases our current understanding of the biology of “Ca. L. solanacearum” and will facilitate future efforts in the bacterial cultivation and host-bacterium interaction research.